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syno:dsm7inst [2026/09/06 15:50] – [KMIP for key management] Bernard Condrausyno:dsm7inst [2026/10/01 12:47] (current) – [Check MailPlus Server connectivity] Bernard Condrau
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   - Open **MailPlus Server** and go to **Mail Delivery --> General**. //Enable SMTP authentication// and disable external postmaster in //External Postmaster//.   - Open **MailPlus Server** and go to **Mail Delivery --> General**. //Enable SMTP authentication// and disable external postmaster in //External Postmaster//.
   - Disable //SMTP-SSL/TLS (port 465)// in **Synology MailPlus Server --> Service**   - Disable //SMTP-SSL/TLS (port 465)// in **Synology MailPlus Server --> Service**
 +
 +===== Check MailPlus Server connectivity =====
 +  * Use the following command from an external source and from within your LAN:<code>openssl s_client -starttls smtp -connect smtp.example.com:587</code>
 +  * If external access works, but LAN access does not, then you have likely run into DNS/hairpin NAT issues. You best solve this by adding your mail host to the host overrides table. In [[pfsense:pfsense|pfSense firewall]] this is at //Services --> DNS Resolver --> General Settings//, scroll down to the bottom of the page.
 +  * You can check this by accessing your SMTP Server from within your LAN by IP address instead of the mail domain name.
 +  * Another good tool to check SMTP accessability is [[https://github.com/keny-studio/terminal-c/blob/main/Swaks%20-%20SMTP%20Testing%20tool.md|swaks]]:<code>sudo apt update
 +sudo apt install swaks
 +swaks --to recipient@example.com \
 +      --from sender@example.com \
 +      --server smtp.example.com \
 +      --port 587 \
 +      --tls \
 +      --auth LOGIN \
 +      --auth-user your_username \
 +      --auth-password your_password</code>
 +  * Make sure your web server who uses your SMTP Server will not get blocked by DSM or MailPlus Server. Go to //MailPlus Server --> Mail Delivery --> Security --> Block/Allow List// and //Control Panel --> Security --> Protection//, check //Block List// and add the web server's IP address to the //Allow List//.
 +
 +===== Developer Guide =====
 +  * [[https://help.synology.com/developer-guide/|Package Developer Guide]]
 +  * [[https://github.com/vletroye/SynoPackages|GitHub SynoPackages]]
 ==== Links ==== ==== Links ====
   * [[https://kb.synology.com/en-id/DSM/tutorial/How_to_migrate_MailPlus_to_another_NAS|How do I migrate MailPlus to another Synology NAS?]]   * [[https://kb.synology.com/en-id/DSM/tutorial/How_to_migrate_MailPlus_to_another_NAS|How do I migrate MailPlus to another Synology NAS?]]

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